package demo01;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

class Animal {

}

class Dog extends Animal {

}

class Cat extends Animal {

}

public class Test01 {
    public static void main(String[] args) {
        List<?> list = new ArrayList<Dog>();
        List<?> list4 = new ArrayList<Object>();
        List<? extends Animal> list1 = new ArrayList<Cat>();
        List<? super Animal> list2 = new ArrayList<Object>();
    }

}
